1. Field of the Invention
The present invention relates to an NC lathe comprising a headstock for rotatably supporting a main spindle for holding a workpiece, and a tool rest for holding a tool, the tool rest being movable in a predetermined feed direction.
2. Description of the Prior Art
Conventionally, a machine tool having a structure shown in FIGS. 7 and 8 is known as an NC lathe. This NC lathe 100 comprises a bed 101 formed in the shape of a triangular prism becoming broad toward the bottom, and a first headstock 102, a second headstock 105, a first tool rest 110, a second tool rest 115 and the like provided on the bed 101 as shown in FIGS. 7 and 8 (refer to Japanese Unexamined Patent Publication No. 2002-59301).
The first and second headstocks 102 and 105 rotatably support main spindles 103 and 106 around the axes thereof, respectively, and are provided with rotation drive devices (not shown) for rotating the main spindles 103 and 106 around the axes thereof. The first and second headstocks 102 and 105 are mounted on the inclined face on the front side of the bed 101. In addition, the second headstock 105 is configured so as to move in the arrow-indicated Z-axis direction under the guidance of first guide rails 108 provided on the inclined face on the front side of the bed 101 in parallel with the axis lines of the main spindles 103 and 106. Furthermore, the main spindles 103 and 106 are provided with chucks 104 and 107 for holding workpieces.
The first tool rest 110 is provided between the first headstock 102 and the second headstock 105 and comprises a saddle 111 configured so as to move in the arrow-indicated Z-axis direction under the guidance of the first guide rails 108, and a tool rest body 112, configured so as to move in the arrow-indicated X-axis direction under the guidance of guide rails (not shown) provided on the saddle 111 orthogonally to the axis lines of the main spindles 103 and 106, for holding tools T.
The second tool rest 115 comprises a column 116 configured so as to move in the arrow-indicated Z-axis direction under the guidance of second guide rails 109 provided on the inclined face on the rear side of the bed 101 in parallel with the axis lines of the main spindles 103 and 106, a support base 117 configured so as to move in the arrow-indicated X-axis direction under the guidance of guide rails (not shown) provided on the column 116 orthogonally to the axis lines of the main spindles 103 and 106, a tool rest body 118, rotatably supported by the support base 117 in the arrow-indicated B-axis direction around a predetermined rotation center axis and configured so that indexing is made possible at a predetermined rotation angle position in the B-axis direction, for rotatably holding a tool T, a drive motor 119, provided on the tool rest body 118, for rotating the tool T, and a storage box 120, installed on the support base 117 so as to protrude toward the front side of the tool rest body 118, for storing the electric wiring of the drive motor 119 and the like.
The second headstock 105, the saddle 111 and the tool rest body 112 of the first tool rest 110, and the column 116 and the support base 117 of the second tool rest 115 are configured so as to be moved in predetermined feed directions by feed devices (not shown) respectively corresponding thereto.
In this NC lathe 100, a workpiece held in the chuck 104 of the first headstock 102 or in the chuck 107 of the second headstock 105 is rotated when the main spindle 103 or 106 is rotated by the rotation drive device (not shown). Furthermore, the first tool rest 110 or the second tool rest 115 in which the tool T is held is moved in a predetermined feed direction by a feed device (not shown). Hence, a relative motion is carried out between the rotating workpiece and the tool T, whereby the workpiece is machined into a predetermined shape.
When the workpiece is machined, the tool T held in the second tool rest 115 is rotated appropriately by the drive motor 119, or the tool rest body 118 is rotated in the B-axis direction with respect to the support base 117 so as to be indexed appropriately at a predetermined rotation angle position in the B-axis direction in accordance with the machining requirements of the workpiece.
Structural members constituting an NC lathe are usually required to have sufficient rigidity so that highly accurate machining can be carried out, and these structural members have considerable weights. Because of the heavy weight of the column 116 serving as a movable body, the above-mentioned conventional NC lathe 100 has problems; that is, the load applied to a drive motor constituting a feed device (not shown) is large, the feed speed thereof cannot be raised, and the column 116 is apt to bend under the influence of inertia at the start and stop of the movement, thereby causing reduction in machining accuracy.
In addition, chips generated during workpiece machining fall down along the inclined face on the front side of the bed 101. Although the first guide rails 108 are appropriately enclosed with a cover (not shown), if chips enter the inside of the cover, the accuracy of the guidance for the second headstock 105 and the first tool rest 110 is lowered.
Furthermore, the bed 101 is formed so as to become broad toward the bottom, and the tool rest body 112 of the first tool rest 110 is movable by a predetermined amount in an obliquely downward direction away from the axis lines of the main spindles 103 and 106 along the X-axis. Hence, the size of the lower end of the bed 101 becomes large naturally, and the distances from the front end of the bed 101 to the main spindles 103 and 106 and the second tool rest 115 are large, thereby causing problems; that is, operator workability is low (it is difficult for the operator to come close to the workpiece machining area), and a wide installation area is required.
Still further, when the tool rest body 118 of the second tool rest 115 is rotated in the B-axis direction, the tool T held in the tool rest body 118 may be hidden behind the storage box 120 depending on the rotation angle position thereof, thereby causing inconvenience; that is, it is difficult for the operator to check the position and state of the tool T.
In view of the above-mentioned circumstances, an object of the present invention is to provide an NC lathe capable of carrying out highly accurate machining and being compact in size and high in operator workability.